Deflection yoke for use in color cathode ray tubes

ABSTRACT

A deflection yoke for color cathode ray tubes, the deflection yoke including a vertical deflection coil for generating a vertical deflecting magnetic field having a barrel-shaped distortion, and a horizontal deflection coil for generating a horizontal deflection magnetic field having a pin-cushion shaped distortion, a differential coil connected to the horizontal deflection coil, a pair of cores located in opposite positions at a smaller rim portion of the yoke, the cores being provided with coils for generating a quadripolar magnetic field, a pick-up coil magnetically coupled to the differential coil or the horizontal deflection coil, and a current waveform shaping circuit for supplying a current to the quadripolar magnetic field generating coils.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a deflection yoke for use in colorcathode ray tubes to produce a magnetic field so as to deflect theelectron beams.

2. Description of the Prior Art

In general, a deflection yoke used in color cathode ray tubes with anin-line type electron gun is designed to produce a pin-cushion shapehorizontal deflection magnetic field and a barrel-shape verticaldeflection magnetic field. This type of yoke, commonly called aself-convergence type, is advantageous in that it does not require acomplex convergence circuit. On the other hand, this type of yoke islikely to involve misconvergence of the pattern as shown in FIGS. 14(a),(b) and (c), owing to an erroneous assembly of the electron gun and/orthe yoke itself. The misconvergences of the pattern shown in FIGS. 14(a)and (b) are caused owing to an axial misalignment, but can be fixed bycorrecting the tilt of the deflection yoke or alternatively either byadjusting a differential coil connected to the horizontal deflectioncoil or a differential resistance connected to the vertical deflectioncoil. In contrast, the misconvergence shown in FIG. 14(c) is causedowing to a rotational misalignment, to which the above-mentionedcorrection methods cannot be applied. In FIGS. 14(a), (b) and (c) theline R represents a lateral red line, the line B represents a lateralblue line, b, g and r represent the sources of electron beams for blue,green and red, respectively.

Japanese Laid-Open Patent Publication No. 60-91536 discloses a means ofcorrecting a misconvergence, which includes a two-pole magnetic ring, afour-pole magnetic ring, and a six-pole magnetic ring, and additionally,another quadripolar magnet ring so as to correct a misconvergence due toa rotational misalignment. There is another method for correctingmisconvergence, which includes a magnetic ring provided in the otherdeflection coil as a magnetic shield whereby an equivalently reversedmisconvergence is deliberately caused.

The known correcting methods of misconvergence described above havedisadvantages, in that, with the first method the two quadripolar magnetrings must be alternately rotated until the correction is effected. Therepetition of the alternate rotation of the magnet rings is likely tounfavorably affect the convergence characteristics in the center of thefluorescent screen. In the second method it is difficult to correct thewhole fluorescent screen.

SUMMARY OF THE INVENTION

The deflection yoke of this invention, which overcomes theabove-discussed and numerous other disadvantages and deficiencies of theprior art, comprises a larger rim portion and a smaller rim portion, avertical deflection coil for generating a vertical deflecting magneticfield having a barrel-shaped distortion, and a horizontal deflectioncoil for generating a horizontal deflection magnetic field having apin-cushion shaped distortion, a differential coil connected to thehorizontal deflection coil, a pair of cores located in oppositepositions at the smaller rim portion, the cores being provided withcoils for generating a quadripolar magnetic field, a pick-up coilmagnetically coupled to the differential coil or the horizontaldeflection coil, and a current waveform shaping circuit for supplying acurrent to the quadripolar magnetic field generating coils.

In a preferred embodiment, the differential coil is wound around thesame bobbin as that for use in the pick-up coil.

In another preferred embodiment, the pick-up coils are located nearwindows of the horizontal deflection coil.

In a further preferred embodiment, the pick-up coils are coupled to therespective ends of the horizontal deflection coil.

In a still further preferred embodiment, the pick-up coils are providedby part of the horizontal deflection coil.

In another preferred embodiment, each of the pair of cores comprises aferrite bar shaped like the letter I or letter U.

In a preferred embodiment, the correction current comprises a half-cycleof positive or negative component of the saw-tooth current.

In another preferred embodiment, the correction current is a parabolicwaveform current.

Thus, the invention described herein makes possible the objects of (1)providing a deflection yoke which makes it easy to correct amisconvergence due to rotational misalignment by adjusting thedeflection yoke, and (2) providing a deflection yoke capable ofcorrecting misconvergence without unfavorably affecting the convergencecharacteristics over the whole fluorescent screen.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention may be better understood and its numerous objects andadvantages will become apparent to those skilled in the art by referenceto the accompanying drawings as follows:

FIG. 1 is a perspective view showing a deflection yoke according to thepresent invention;

FIG. 2 is a rear view showing the deflection yoke of FIG. 1;

FIG. 3 is a circuit diagram showing a horizontal deflection magneticfield of the yoke of FIG. 1;

FIGS. 4(a) and (b) are diagrammatic views showing the waveform of pulsevoltage induced in the pick-up coil of the circuit and the waveform of acurrent flowing through a coil for generating a quadripolar magneticfield;

FIG. 5 is an explanatory view illustrating the relationship between thequadripolar magnetic field and the electron beam;

FIG. 6 is a diagrammatic view showing directions in which the lateralred and blue lines on the screen are subjected to deflection by thequadripolar magnetic field;

FIG. 7 is a diagram showing a circuit for shaping a current waveform;

FIGS. 8 to 10 are diagrammatic views showing the relationship betweenthe pick-up coil and the horizontal deflection coil in each embodiment;

FIG. 11 is a diagrammatic view showing a parabolic waveform of acurrent;

FIGS. 12 and 13 are diagrammatic rear views showing a positionalrelationship between a coil for generating a quadripolar magnetic fieldand a core of the coil in a preferred embodiment; and

FIGS. 14(a), (b) and (c) are diagrammatic views showing patterns ofmisconvergence.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, there is provided a deflection yoke 5 whichincludes a pair of saddle-type horizontal deflection coils 1a and 1b, apair of toroidal type vertical deflection coils 2a and 2b having aferrite core 3, and an insulating frame 4 of synthetic resin.

The deflection yoke 5 is provided with a pair of differential coils 7aand 7b mounted on a printed board 6, a circuit element 8 adapted toshape a waveform of a current, and a pair of ferrite cores 10a and 10bshaped like the letter I around which coils 9a and 9b are wound togenerate a quadripolar magnetic field.

The differential coils 7a and 7b are wound around a bobbin 11, aroundwhich a pick-up coil 12 is also wound. The pick-up coil 12,electromagnetically coupled to the differential coils 7a and 7b, isconnected to the coils 9a and 9b through a circuit 8, which is to shapethe waveform of a current as shown in FIG. 3.

When a current passes through the pair of horizontal deflection coils 1aand 1b and the pair of deflection coils 7a and 7b, a pulse voltage asshown in FIG. 4(a) is induced in the pick-up coil 12. The waveform ofthis pulse voltage is shaped by a waveform shaping circuit, whichincludes a coil, a resistance and a diode. As a result, it is shapedinto a sawtooth waveform current as shown in FIG. 4(b) (synchronous withthe horizontal deflection cycle), and flows through the coils 9a and 9b.

This saw-tooth current flows through the coils 9a and 9b only for a halfcycle period during which the left-hand portion of the screen is scannedby beam, and the resulting quadripolar magnetic field acts on theelectron beams b and r at opposite sides as indicated by dotted lines inFIG. 5. The electron beams b and r are subjected to upward and downwardforces in the directions of large arrows in FIG. 5, and the red line Rand the blue line B are deflected in the direction of the arrows. Asshown in FIG. 14(c), the direction of this deflection is opposite tothat of the misconvergence due to a rotational misalignment. Thus, themisconvergence shown in FIG. 14(c) is converted into a misconvergence ofthe pattern shown in FIG. 14(b). The misconvergence converted in thisway is corrected by adjusting the coils 7a and 7b in a known manner.

If any pattern opposite to that shown in FIG. 14(c) occurs in which thelateral blue line B appears below the lateral red line R around aperipheral portion of the fluorescent screen, the misconvergence can becorrected by reversing the flowing direction of a current flowingthrough the coils 9a and 9b in the current waveform shaping circuit.

Referring to FIGS. 7 to 10, various examples of the current waveformshaping circuit 8 will be described:

Generally, the circuit 8 is constructed as shown in FIG. 7. In theabove-mentioned embodiment the pick-up coils 12 are wound around thebobbin 11 for use in the differential coil 7a and 7b. Alternatively, asshown in FIG. 8, the pick-up coils 12 can be provided near the windowsof the horizontal deflection coils 1a and 1b, thereby securing theelectromagnetic coupling therebetween. FIG. 9 shows another modificationin which the pick-up coils 12 are respectively wound around a forwardarched portion and a backward arched portion of the horizontaldeflection coil, thereby securing the electromagnetic connectiontherebetween. FIG. 10 shows a further modification in which a pluralityof conductors are wound into horizontal deflection coils, one of whichis used as a pick-up coil.

In the foregoing description the quadripolar magnetic field is generatedin the left-hand half portion of the screen, but it is possible togenerate it in the right-hand half portion thereof. Instead of thesaw-tooth waveform, a parabolic current as shown in FIG. 11 can begenerated in an integration circuit so that the left-hand and right-handportions of the screen are simultaneously corrected. The pair of coreswith coils can be provided in horizontally opposite positions as shownin FIG. 12. A generally U-shaped cores as shown in FIG. 13 can be used.

It is understood that various other modifications will be apparent toand can be readily made by those skilled in the art without departingfrom the scope and spirit of this invention. Accordingly, it is notintended that the scope of the claims appended hereto be limited to thedescription as set forth herein, but rather that the claims be construedas encompassing all the features of patentable novelty that reside inthe present invention, including all features that would be treated asequivalents thereof by those skilled in the art to which this inventionpertains.

What is claimed is:
 1. A deflection yoke for use in color cathode raytubes, the deflection yoke comprising a larger rim portion and a smallerrim portion, a vertical deflection coil for generating a verticaldeflecting magnetic field having a barrel-shaped distortion, and ahorizontal deflection coil for generating a horizontal deflectionmagnetic field having a pin-cushion shaped distortion, a differentialcoil connected to the horizontal deflection coil, a pair of coreslocated in opposite positions in relation to the smaller rim portion,the cores being provided with coils for generating a quadripolarmagnetic field, a pickup coil magnetically coupled to one of thedifferential coil and the horizontal deflection coil, and a currentwaveform shaping circuit for supplying a current to the quadripolarmagnetic field generating coils.
 2. A deflection yoke according to claim1, wherein the differential coil is wound around the same bobbin as thatfor use in the pick-up coil.
 3. A deflection yoke according to claim 1,wherein the .[∂]. .Iadd.pick-up .Iaddend.coil is located near.[.windows.]. .Iadd.a window .Iaddend.of the horizontal deflection coil.4. A deflection yoke according to claim 1, wherein the .[∂]..Iadd.pick-up .Iaddend.coil is coupled to .[.the respective ends.]..Iadd.an arched portion .Iaddend.of the horizontal deflection coil.
 5. Adeflection yoke according to claim 1, wherein the .[∂]. .Iadd.pick-up.Iaddend.coil is provided by part of the horizontal deflection coil. 6.A deflection yoke according to claim 1, wherein each of the pair ofcores comprises a ferrite bar shaped like the letter I.
 7. A deflectionyoke according to claim 1, wherein the each of the pair of corescomprises a ferrite bar shaped like the letter U.
 8. A deflection yokeaccording to claim 1, wherein the correction current comprises ahalf-cycle of the saw-tooth current.
 9. A deflection yoke according toclaim 1, wherein the correction current is a parabolic waveform current.